netdev - Re: BUILD_BUG_ON error in mlx5/core/pagealloc.c

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Date:   Mon, 10 Oct 2016 17:10:15 -0700
From:   Tom Herbert <tom@...bertland.com>
To:     Linux Kernel Network Developers <netdev@...r.kernel.org>,
        Saeed Mahameed <saeedm@...lanox.com>
Subject: Re: BUILD_BUG_ON error in mlx5/core/pagealloc.c

On Mon, Oct 10, 2016 at 4:41 PM, Tom Herbert <tom@...bertland.com> wrote:
> I am hitting this in mlx5
>
> drivers/net/ethernet/mellanox/mlx5/core/pagealloc.c: In function
> ‘reclaim_pages_cmd.clone.0’:
> drivers/net/ethernet/mellanox/mlx5/core/pagealloc.c:346: error: call
> to ‘__compiletime_assert_346’ declared with attribute error:
> BUILD_BUG_ON failed: __mlx5_bit_off(manage_pages_out, pas[i]) % 64
> drivers/net/ethernet/mellanox/mlx5/core/pagealloc.c: In function ‘give_pages’:
> drivers/net/ethernet/mellanox/mlx5/core/pagealloc.c:291: error: call
> to ‘__compiletime_assert_291’ declared with attribute error:
> BUILD_BUG_ON failed: __mlx5_bit_off(manage_pages_in, pas[i]) % 64
>

The expression in BUILD_BUG_ON expands to "((unsigned)(unsigned
long)(&(((struct mlx5_ifc_manage_pages_in_bits *)0)->pas[i]))) % 64".
The variable array index to pas makes this expression non-constant, I
imagine that is where the problem lies.

> Bisecting points to:
>
> commit a533ed5e179cd15512d40282617909d3482a771c
> Author: Saeed Mahameed <saeedm@...lanox.com>
> Date:   Sun Jul 17 13:27:25 2016 +0300
>
>     net/mlx5: Pages management commands via mlx5 ifc
>
> Thanks,
> Tom